Cook the quinoa. Rinse 1 cup quinoa under cold water. Add to a pot with 2 cups broth or water and a pinch of salt.
Bring to a boil, reduce heat, cover, and simmer for 15 minutes. Remove from heat, keep covered for 5 minutes, then fluff.
Sauté aromatics. In a large skillet over medium heat, add 1–2 tablespoons olive oil. Cook the diced onion with a pinch of salt for 5–6 minutes until soft and lightly golden.
Stir in the minced garlic and cook 30 seconds until fragrant.
Bloom the spices. Add tomato paste, cumin, smoked paprika, chili powder, and coriander. Stir for 1 minute to toast the spices and deepen the flavor. If the pan looks dry, add a splash of oil or water.
Add the beans. Stir in the black beans with 1/3 cup water.
Simmer 3–4 minutes, smashing some beans with a spoon to thicken. Season with salt, pepper, and a pinch of red pepper flakes if you like heat.
Combine with quinoa. Fold the cooked quinoa into the skillet until evenly mixed. Squeeze in the juice of 1 lime and a teaspoon of honey or maple syrup to round out the spices.
Taste and adjust seasoning.
Make the quick slaw. In a bowl, toss shredded cabbage with the juice of 1 lime, a drizzle of olive oil, a pinch of salt, and half the chopped cilantro. Let it sit while you warm the tortillas.
Warm the tortillas. Heat a dry skillet over medium-high. Warm each tortilla 30 seconds per side until soft and slightly charred.
Keep them wrapped in a clean towel to stay pliable.
Assemble the tacos. Fill tortillas with the bean-quinoa mixture. Top with lime slaw, avocado slices, extra cilantro, and any optional toppings. Finish with a squeeze of lime and a few drops of hot sauce if you like.
Serve. Plate with lime wedges on the side and enjoy while warm.